1. Field of the Invention
The present invention relates to an image forming device, and more particularly, relates to a paper feeding apparatus for use in an image forming device and a paper feeding method thereof.
2. Related Art
Generally, an image forming device, such as a printer, a copier, a facsimile machine and a multi-functional product, is equipped with a paper feeding cassette for accommodating a stack of printable media, such as paper sheets to be used when forming images. The paper feeding cassette is detachably or slidably mounted in a main body of an image forming device so that it is entirely or partially exposed outside the main body whenever new paper sheets are loaded therein or paper sheets accommodated in the cassette are replaced with new ones.
The paper feeding cassette can be classified into a single-size cassette in which only a single size of paper can be loaded therein, and a universal cassette in which a variety size of paper sheets can be loaded therein and adjustment can be made to accommodate paper sheets of a different size.
The single-size cassette has the advantage in that paper sheets can be reliably fed into an image forming device with little or no errors, since a paper size of the cassette is fixedly set; however, such a single-size cassette also has the disadvantage in that multiple cassettes are necessary, if paper sheets of different sizes are to be fed into the image forming device. As a result, a large storage space is required to store a large number of cassettes. In addition, there is another disadvantage in that the cassette mounted in an image forming device should be inconveniently replaced with another cassette whenever an image is needed to be formed on a paper sheet of a different size.
In contrast to the single-size cassette, a universal cassette is more desirable and is widely used to accommodate paper sheets of a variety of sizes for use in an image forming device.
FIG. 1 illustrates a typical universal cassette 1 having a side guide part used for setting a lateral size of paper sheets and guiding sides of the paper sheets, and a rear guide part used for setting a longitudinal size of paper sheets and guiding rear ends of the paper sheets.
The universal cassette 1 includes a casing 10, a knock-up plate 12 coupled to both sides of the casing 10, via pins 13, such that it is pivotable in the vertical direction for receiving paper sheets thereon, a side guide part 14 having a pair of side guides installed in the casing 10 such that it is slidably moved in the lateral direction of the paper sheets, while supporting both side edges of the paper sheets placed on the knock-up plate 12, a rear guide part 16 installed in the casing 10 such that it conducts a serration movement in the longitudinal direction of the paper sheets, while supporting rear edges of the paper sheets placed on the knock-up plate 12, and a pair of finger members 17 for pressing down front corners of the paper sheets guided by the side guide part 14 and the rear guide part 16 and placed on the knock-up plate 12.
A spring 18 is provided under the knock-up plate 12 for pushing up the knock-up plate 12 as the paper sheets are being fed into the image forming device. Further, a rack 15 is provided under the side guide part 14; and a pinion (not shown) is disposed between the rack 15 and the side guide part 14 and geared with the rack 15 and the side guide part 14 for facilitating the side guide part 14 to move slidably.
Hereinafter, the paper load and replacement operations for the conventional universal cassette 1 will be described in detail as follows.
First, the universal cassette 1 is separated from its mount position in a main body of an image forming device and moved to be exposed entirely or partially so that paper sheets can be loaded or replaced.
Next, the side guides of the side guide part 14 are adjusted to be disposed far away enough from each other so that paper sheets can be easily introduced into the cassette 1, and paper sheets are newly introduced into the cassette 1 or the paper sheets accommodated in the cassette 1 are replaced with new ones.
After introduction or replacement of paper sheets, the side guide part 14 is moved in the direction of an arrow “I”, thereby supporting both sides of the paper sheets. The rear guide part 16 is moved in the direction of an arrow “H”, thereby supporting rear ends of the paper sheets.
In this instance, the front ends of the paper sheets are adjusted to be aligned with a front end of the knock-up plate 12, and the front ends of the paper sheets are interposed between the knock-up plate 12 and the finger members 17.
The introduced paper sheets in the above described manner are in ready to be fed into the image forming device, when an uppermost paper sheet is pressed against the finger members 17 due to an elastic force of the spring 18 installed under the knock-up plate 12.
Finally, the universal cassette 1 is mounted again in the main body of the image forming device after the paper sheets are loaded in the cassette 1.
However, such a conventional universal cassette 1 has the following disadvantages. First, since position of the rear guide part 16 is adjusted by a serration motion when setting a paper accommodation size of the cassette 1, it is difficult to move the rear guide part 16. Second, in the case in which the universal cassette 1 accommodates paper sheets having a smaller size than the largest size that can be accommodated in the cassette 1, for example, the universal cassette 1 accommodates paper sheets having a half size of the largest size, there can be an empty space in the universal cassette 1, particularly at a rear side of the accommodated paper sheets. However, such an empty space remains unused. Even if a redundant empty space at a rear side of the cassette 1 is used, that is, in case of accommodating paper sheets even in the redundant empty space, the paper sheets accommodated in the redundant empty space can be fed into the image forming device after paper sheets accommodated at the front portion of the cassette 1 are run out. Accordingly, the number of paper supply times can be made smaller, resulting in avoidance of inconvenience of supplying paper sheets frequently. However, the above described paper accommodation technique can not be applied to the conventional universal cassette 1.